Owing to the development of the information industry, techniques for transmitting a large amount of data of various types at high rates are required. In this context, a DAS is under study to eliminate shadowing areas and extend coverage by distributing a plurality of antennas across an existing cell.
The DAS is a system that uses a plurality of distributed antennas connected to a single Base Station (BS) by cable or by a dedicated line. The single BS manages the antennas distributed at various positions in the cell. The DAS is different from a Centralized Antenna System (CAS) having a plurality of BS antennas at the center of a cell, in that a plurality of antennas are distributed across a cell. The DAS system is also different from a femto cell in that the BS at the center of the cell manages all distributed antenna areas within the cell, rather than each individual distributed antenna unit manages its antenna area. Compared to a multi-hop relay system in which a BS is connected wirelessly to a Remote Station (RS), or an ad-hoc network, the distributed antenna units are connected to the BS by cable or a dedicated line in the DAS. While a repeater is configured so as to simply amplify a signal and transmit the amplified signal, each distributed antenna can transmit a different signal in response to a command from the BS in the DAS.
Considering that distributed antennas can support a single or multiple Mobile Stations (MSs) by transmitting and receiving different data streams at the same time, the DAS may be regarded as a kind of Multiple Input Multiple Output (MIMO) system. From the standpoint of the MIMO system, the DAS can reduce transmission power because each of antennas distributed across a cell has a smaller transmission area than in the CAS. The reduction of path loss attributed to a shorter transmission distance between an antenna and an MS enables high-speed data transmission, thereby increasing the transmission capacity and power efficiency of a cellular system and keeping communication performance uniform irrespective of the location of a user in the cell, relative to the CAS. Furthermore, as a plurality of distributed antennas are connected to a BS by cable or a dedicated line, signal loss is small and the correlation and interference between antennas are decreased. As a consequence, high Signal to Interference plus Noise Ratio (SINR) can be achieved.
As described above, the DAS may be a new foundation for cellular communication, substituting for the conventional CAS because it can reduce BS installation cost and backhaul maintenance cost, extend service coverage, and increase SINR in a future-generation mobile communication system.
Accordingly, there exists a need for supporting the DAS as well as the CAS with CAS-based communication standards in a conventional mobile communication system.